Discharge lamp cathode



Oct. 3, 1961 R. B. THOMAS 3,003,077

DISCHARGE LAMP CATHODE Original Filed July 10. 1953 RALPH B. THOMAS,

INVENTOR ATTORNEY -m-- Anna. e... "um..." has.

3,003,077 DISCHARGE LAMP CATHODE Ralph B. Thomas, Salem, Mass, assignor, hy-mesneassignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware. Continuation of application Ser. No. 367,205, zluly 10, 1953. This application Nov. 14, 1958, Ser. No. 773,57

Claims. (0.3131343) This invention rel-ates to electric discharge lamps, and particularly to cathodes therefor.

Such cathodes usually comprise a coiled-coil filament carrying a filling of electron emissive material, such as h al ali e r de n i min r soil I o cases, and especially in so-called instant-start fluorescent lamps, an additional coil of very fine wire extends around the circumference of the wire of the coiled-coil, the latter Wi n a g a a p m nen mandre fo t fi co l h i i al i b ing v y 11. to nsure its quiq heating by the discharge when the lamp is started, a composite coil is generally called a triple-coil, although only the fine wire overwinding is triply-coiled.

Such coils require a larger number of winding machines for their manufacture in quantity production because of the large number of turns of the hire wire, and are hence quite expensive to manufacture. According to one aspect of the present invention, the number of winding machines required can be greatly reduced by winding several wires together in parallel simultaneously onto the mandrel wire, so that the fine winding on the wire becomes a stranded cable of several fine wires. For example, the use of six such wires wound together would reduce the number of machines required not only by six, due to the multiple number of coils, but actually by a factor of seven and one-half, because the pitch angle of the fine wire with the mandrel wire is increased, as will be explained in the following specification. All six wires can be wound simultaneously on a single machine by providing six separate bobbins of wire in the winding head and six separate guides for the wire, instead of the usual single bobbin and single guide.

In accordance with a further aspect of the invention, this mandrel wire may be removed so that the final coil is, for example, a coiled-coil of stranded wire having a hollow core and spaced strands. The wires can be made of somewhat larger diameter than would be used if the mandrel were not removed from the coil, and the net effect, in the final coiling itself, because of the low pitch angle, is to produce a coil from a stranded cable, said cable having a hollow core, with the strands spaced from each other.

The strands. being in effect connected in multiple, the resistance of the composite winding will be much less than that of a single coil of the same fine wire.

The rigidity of the resultant coil will be increased over the rigidity of a single-wire coil of the same size wire and same total number of turns, because of the decreased pitch angle.

Other features, advantages and objects of the inven tion will be apparent from the following specification, taken with the accompanying drawings, in which:

FIGURE 1 is a view of a 4-wire cable after stranding, with the first mandrel still in place;

FIGURE 2 is a view of the first coiling of the resultant stranded cable, with the first and second mandrels in lace; p FIGURE 3 is a view of the second coiling, with the first, second and third mandrels in place;

FIGURE 4 is a View of the coil with all mandrels removed, and an electron-emissive coating applied, part of the coating being shown broken away so that the coil is visible.

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t the w res Z. an a lane r ns e se 9 memendrel 5.

I he o l omprise o l min w e. wi h, h s pasms be ween. adja en hints s. t n he quad upl w s e strewn thewi auld cros he ma d e m s t a erse y. and t e Pitsh al e e quld be ma 1 th l of FIGURE 1, ho e 1 t u qe v turns o t se g i 1 a e di eat ch othe b instead have three turns of the other wires 2, 3, 4-, between them; time the Pitq n l s crea e a has ha h h single coil wouldh w h u me the spacing plus the sum of three wire diameters, betw n a e rn he ire 3 4 m me mor n ar P ra to h ma d e w r an his in r ase he idi y sufli ien y t0 remi t e mi ien of h man el nzth fina will he eb P o din mor room for holding e ss ni sive mate i l ithin he turn Although various dimensions and wire sizes can be used in the coil of FIGURE 1, the wires 1, 2, 3, 4- in one specific example, had a diameter of 1.25 mils, and were of tungsten, four such wires being used as in the figure. The mandrel 5 was of 2.5 mil molybdenum wire. The pitch angle was 59, and there were 51 turns of each wire per inch, or 204 total turns per inch, including the turns of all four tungsten wires 1, 2, 3, 4. The result of this first Winding is therefore a stranded cable having a hollow core, its component strands being in general spaced from each other.

FIGURE 2 shows the stranded wire of FIG. 1, including the mandrel 5, wound around another mandrel 6 of larger diameter. As an example, the coil specifically described in connection with FIGURE 1 was wound on a 9-mil molybdenum mandrel, with turns per inch.

The resultant coil was then annealed in wet hydrogen at about 1550 C. for a period of about 5 or 6 seconds, and was then wound around a 26-mil steel mandrel 7, as in FIG. 3, at 28 turns-per inch, the steel mandrel being afterward mechanically pulled out of the coil. The winding for this third coiling was done on the usual type of retractable-mandrel winding machine ordinarily used for the final winding of coiled-coil filaments for lamps.

The molybdenum mandrels 5 and 6 still remained in the coil after the steel mandrel 7 was removed, but after the coil had been annealed in dry hydrogen for 10 minutes at about 1500 C., they were then removed, in the manner customary for removing such mandrels, that is by being dissolved out in an acid solution which removes the molybdenum without removing the tungsten, for example, a solution of four parts nitric acid and one part sulfuric acid, as shown in US. Patent 1,650,605, granted November 29, 192.7, to P. A. Campbell.

The resultant coil 8 was then mounted on the lead-in wires 9, 10, which had been scaled through the glass stem 10, as shown in FIGURE 5. A coating or filling 11 of the carbonates of calcium, strontium, and barium was applied to the coil in the usual manner, the excess in the larger coil being blown off, so that the carbonate was held within the stranded wire and in the minor coils but did not extend to the turns of the major coil.

The stem 12 was then sealed to an end of glass tube 13, there being a similar stem at the other end also. The tube 13 was exhausted through exhaust tubulation 14 in the usual manner, the carbonates 11 on the coil being changed to oxides by heating during exhaust. The

exhaust tubulation 14, which is in communication with the inside of the tube 13 through the side of the stem 12 in the customary manner, was then sealed off by heating it to eflect closure thereof and to separate it from the exhaust system. The lead-in wires extend to contact prongs 15, 16 in the insulating base 17, cemented to the tube 13.

Although four wires 1, 2, 3, 4 are shown in the figures for convenience, a smaller or lesser number 1, n, can be used.

This application is a continuation of my application Serial No. 367,205, filed July 10, 1953, which was copending with this application and is now abandoned.

What I claim is:

l. A cathode for an electric discharge device, said cathode comprising a doubly-coiled mandrel-free stranded cable, the stranded cable having a hollow core and the strands being wire in general spaced from and parallel to each other, the angle of the strands with respect to the axis of the cable being low so that the strands are nearly parallel to said axis.

2. A cathode for an electric discharge device, said cathode comprising a doubly-coiled mandrel-free stranded cable, the stranded cable having a hollow core and the strands being wires in general spaced from and parallel to each other, and a filling of electron-emitting material within the otherwise hollow core, the angle of the strands with respect to the axis of the cable being low so that the strands are nearly parallel to said axis.

3. A cathode for an electric discharge device, said cathode comprising a mandrel-free stranded cable, having a hollow core with the strands being wires in general spaced from and parallel to each other, said stranded cable being doubly coiled to have a major and a minor coil, and a filling of electron-emissive substance within Said otherwise hollow core and within said minor coil, the angle of the strands with respect to the axis of the cable being low so that the strands are nearly parallel to said axis.

4. A cathode for an electric discharge device, said cathode comprising a mandrel-free stranded cable, having a hollow core with the strands being wires in general spaced from and parallel to each other, said stranded cable being doubly coiled to have a major and a minor coil, and a filling of electron-emissive substance within said otherwise hollow core and within said minor coil,

but being absent from the region outside said minor coil,

sive substance is a powder of at least one of the alkaline earth oxides.

References Cited in the file of this patent UNITED STATES PATENTS Lemmers Dec. 18, 1956 Penon Jan. 21, 1958 

